High levels of toxic blue-green algae have been detected. A Public Health Warning indicates that water conditions are unsafe and direct water contact (wading, skiing and swimming) should be prohibited.
Kansas public waters currently under a Warning status:

Marion Reservoir (Separate from Marion County Lake), Marion County Memorial Park Lake (Veteran's Lake), Barton County Milford Reservoir (Partial Warning: North of Farnum Creek), Clay, Geary and Dickinson Counties South Park Lake, Johnson County Lake Warnock (Atchison City Lake), Atchison County Cedar Brook Pond, Sedgwick County  
When a Warning is issued, KDHE recommends the following precautions be taken:

Humans, pets and livestock do not drink lake water Water contact should be prohibited. Avoid swimming, wading or other activities with full body contact of lake water Clean fish and rinse with clean water, consume only the fillet portion, and discard all other parts Do not allow pets to eat dried algae If lake water contacts skin or pet fur, wash with clean potable water as soon as possible Avoid areas of visible algae accumulation